There is no shortage of Intel-based laptops. And there are not a few AMD-based laptops. And Apple has their (formerly PPC-based, now Intel-based) laptops. But:

Why are their no readily available laptops built on a MIPS or a SPARC processor, or even a VIA (even though they are still x86). At best, I have found a couple, but they are all like 7"! How about a full-sized version - at least 15.4".

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And the WORD was made flesh, and dwelt among us. (John 1:14)

Youch! Those tadpoles are expensive (though I can't say I'm surprised since it is a SPARC).

I have seen those Chinese models and I looked at the Sharp's and they don't fit the bill if you read my first post - they are too small!!! I mean a 7" or 8.4" screen (and most don't even fill the whole 7" lid). I'm sure there are some who just love those teensy tiny screens and keyboards, but I'm not one of them.

Why can't they make a regular sized laptop?! I've read talk about an ARM laptop that is 15.4" but I haven't seen it for retail. Seeing how ARM came up with an asynchronous processor (I saw some news starting around 2005 I think), that is able to independently shut down unused systems, that would be an awesome laptop processor.

I know that VIA is x86, but again, I mentioned them because they a) aren't widely marketed and b) seem like a good laptop option.

The number 1 beef I have is that all the options I have seen for retail currently (aside from the expensive tadpoles and discontinued models) are microscopic - like I said, 7" or 8.4"! I am not a Lilliputian!

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And the WORD was made flesh, and dwelt among us. (John 1:14)

I suspect the answer to your question is more market-oriented as opposed to any reason related to engineering. Numerous urban legends surround how Intel's marketing practices kick in when any of the big players were rumoured to be offering AMD-based laptops. Given how desktop & laptop manufacturing costs have to be manically watched given the margins manufacturers get are razor-thin, any salesman walking into the door who can promise a cheaper price on processors won't be waiting long before being ushered into some VP's office.

As for your question on sub-10" laptop market (dubbed netbooks, BTW...), the reason the laptop manufacturing houses are clambering to build them is because they are selling exceedingly well in a slumping market. I have two, & they fill the needs I wanted them for better than a 15" laptop, & the price for each was less than $500US. Yes, they are cramped, but neither are they or would I recommend them to be a primary laptop. Yet as secondary laptops, they are quite handy, & they run OpenBSD quite well.

There is no shortage of Intel-based laptops. And there are not a few AMD-based laptops. And Apple has their (formerly PPC-based, now Intel-based) laptops. But:

Why are their no readily available laptops built on a MIPS or a SPARC processor, or even a VIA (even though they are still x86). At best, I have found a couple, but they are all like 7"! How about a full-sized version - at least 15.4".

It is not true that there are no laptops build on a MIPS and SPARC architecture!!!

You got semi-accurate account on laptops based on SPARC 64 processors.
In reality even SUN's own Ultra 3 mobile work station could be considered a laptop as long as you do not try to hold her really on your lap due to the
excessive heat.
The others have already pointed out that Tadpole Computer of Cupertino
and Taiwanese Nature Worldwide Technology.are specialized in Sparc laptops. The General Dynamics sells Tadpole sparc based laptops as their own brand